Pakistan Journal of Marine Sciences, Vol.4(2), 127-131, 1995. FECUNDITY OF THE INDIAN HORSESHOE CRAB, TACHYPLEUS GIGAS (MULLER) FROM BALRAMGARI (ORISSA) Anil Chatterji National In.stitute of Oceanography, Dona Paula, Goa- 403 004, India. ABSTRACT: In Tachypleus gigas (Muller) the fecundity varied from 1242 to 6565 with a mean of 3758±1962. Maximum fecundity was recorded in T. gigas ranging in carapace length between 161 and 170 mm. The ova diameter was between the range of L54 and 2.09 mm with a mean modal value of 1.81 mm. The mean number of ova per mm carapace length, per g body mass and per g ovary mass were 22±12.8, 7±2.0 and 27±3.3 respectively. Linear relationships were obtained between fecundity, carapace length, body mass and ovary mass of T. gigas. KEY WORDS: Tachypleus gigas -fecundity. INTRODUCTION There are two species of the horseshoe crab commonly found along the north-east coast of India (Chatterji and Parulekar, 1992). The one Tachypleus gigas (Muller) occurred abundantly along the coast of Orissa. Th~ horseshoe crab is considered to be an important source for the preparation of a valuable diagnostic reagent from the blue blood that is useful in the detection of gram-negative bacteria associated with pharmaceutical and food products (Rudloe, 1979). Inspite of this economic importance, no information is available on the eco-biology ofthis aquatic animal The estimation of fecundity of a particular species helps in the study of recruitment pattern of the species in a particular environment. The relationship between fecundity and the carapace length is also important for accurately calculating the potential number of eggs, an animal may lay. Considering this important aspect, an attempt has been made in the present paper to estimate the fecundity oft. gigas. MATERIALS AND METHODS Horseshoe crabs (Tachypleus gigas) of both sexes (215 males of 101 to 130 mm carapace length and 220 females of 98 to 246 mm) were collected from the breeding beach at Balramgari (21 27'N; 87 04 'E) (Fig. I). The animals were hand picked during high tides. After collection, the carapace length of each of the specimens was measured and the crabs were divided into eight size groups (I:90-lOO;-II:l01-HO; III:H0-120; IV:l21-130; V:l30-140; VI:141-150; VII:l51-160; VIII:161-170 mm). The ovaries from mature females (121 to 246 mm carapace length) were dissected, weighed and preserved in 5% formaldehyde solution for further analysis. The fecundity estimation was made using the gravimetric method (Chatterji and Parulekar, 1992). Diameter of approximately 200 ova was measured under a Projectina microscope. Gonado-somatic index (gonad mass expressed as percentage of body mass), and mean number of ova per mm carapace length, per g body mass and per g ovary mass ovary in each size group, were calculated (Chatterji and Ansari, 1982).
128 Pakistan Journal of Marine Sciences, VoL4(2), 1995. RESULTS The fecundity of 215 ripe females ranged from 1242 to 6565 with a mean of 3748±1962. The mean number ofova per mm carapace length, per g body mass and per g ovary mass were 22±12.8, 7±2.0 and 27±3.3 respectively. The number of ova increased with an increase in carapace length and body mass but the number of ova per g ovary mass decreased progresively with an increase in the size of the carapace (Table 1). The gonado- somatic index increased considerably with the increase in the size of the crab. Maximum value of gonado-somatic in4ex (29.11) was recorded in size group VIII (carapace length 161-170 mm) (Table 1). A relationship between the carapace length, body mass, mean ovary mass and fecundity is shown in Fig.2. Maximum fecundity was in the largest crabs (size group VIII), where highest values of body and ovary mass were recorded (Fig.2). The diameter of ova varied from 1.54 to 2.09 mm with a mean modal value of 1.81 mm in size groups III to VIII (Fig.3). DISCUSSION The breeding activity in T. gigas has been reported to be throughout the year and mating pairs move on the shore for spawning in conincident with lunar phase and tide height (Chatterji 1994). Maximum fecundity oft. gigas was 6565 which is slightly lower than the maximum (10 982 eggs) reported for Carcinoscorpius rotundicauda (Chatterji and Parulekar, 1992), but much lower the 80 000 eggs being produced by Limulus polyphemus from Delaware Bay (Novitsky, 1984). The variation in the fecundity is dependent on the carapace length, body mass and growth of the animal (Chatterji and Parulekar, 1992). InT. gigas, the number of ova is not found to increase much in proportion to the body mass (14.7% increase) and ovary mass (7.40% decrease). In C. rotundicauda, increase in the number of ova with body mass and carapace length of the crab is more conspicuous than in T. gigas (Chatterji. and Parulekar, 1992). The average number of eggs has also been found to increase with increasing size in the swimming crab, Ovalis punctatus (Preez and McLachlan, 1984). In lighter ovaries the number of ova per g mass was found to be more as compared to the heavier oyaries. This shows that fecundity in T. gigas follows the same pattern as reported in other crabs. While calculating the gonado-somatic index it was found that the weight of ovary increased with the body mass of T. gigas and maximum value calculated in the crab weighing between 161 and 170 mm. The ovary mass and body mass was observed to be more closely related parameters as compared to the carapace length ofthe T. gigas. Fecundity in marine animals varies from individual to individual and shows a close relatioship with the environmental variability (Nikolskii, 1969). But in a particular ecosytem, the influence of environmental factors on the biological activity is a complex phenomenon. As such, it is difficult to assess exactly the influence of a particular environmental factor on the fecundity. of the horseshoe crab. It is also generally believed that availability of a particular food items and temperature of the environment control the fecundity of an animal.
Chatterji: Fecundity of Indian horseshoe crab 129 Table I. Gonado-somatic index and ova counts at various size range oft. gigas. Groups Carapace length Gonado-somatic No. of ova/mm No. of ova/g body No. of ova/g ovary (mm) Index carapace length mass mass (Mean) (Mean) (Mean) I 121-130 18.03 7 4 32 II 131-140 18.37 12 5 29 III 141-150 23.78 16 7 28 IV 151-160 27.66 34 9 26 v 161-170 29.11 40 9 22 I 30 B A Y OF BE 6 A L 21 26~~~~~------~------~~--~~------~ e7 E 2' 3' 4' s' Fig.l. Map showing the cohection site.
130 Pakistan Journal of Marine Sciences, Vol.4(2), 1995. 750 100 thio 0 Body men <m cn vgl~m&j A Ovary mass(ml!lan vah1111) 1 - f'i!icuiidlty roo 500.. 450 0 350 E 200 150 18 100 14 Slu groups (mm_) Fig.2. Relationships between fecundity, body mass and ovary mass with size groups oft. gigas. Carapace Lerogtll(m m I Fig.3. Ova diameter frequencies in mature T. gigas (1 = 1.54-1.67, 2 = 1.68-1.81, 3 = 1.82-1.95, 4 ~ 1.96-2.09 mm).
Chatterji: Fecundity of Indian horseshoe crab 131 There are evidences available which show that the size of the egg of an individual is not affected by the availability of a specific type of food material (Weeks and Quattro, 1991). Th~ size of the egg oft. gigas is between 1.54 and 2.09 mm with an average model value of 1.81 mm whereas, in C. rotundicauda the ova size varies from 1.59 to 2.35 mm. (Chatterji and Parulekar, 1992). This shows that the ova diameter in T. gigas is relatively smaller than C. rotundicauda. ACKNOWLEDGEMENTS The authors are thankful to the Director, N.I.O., Goa for facidies and to Department of Ocean Development, New Delhi for providing financial assistance. REFERENCES Chattelji, A. and Z.A. Ansari. 1982. Fecundity of dolphin fish, CorypluJelUl hippurus L. MaluJsagar- Bulletin of the National.Institute of Oceanography 15: 129-133. Chattelji, A. and A.H. Parulekar. 1992. Fecundity of the Indian horseshoe crab, Carcinoscorpius rotundicauda (Latreille). Tropical Ecology 33: 97-102. Chattelji, A. 1994. The Horseshoe Crab -A Living Fossil Project Swarnjya Publication, Cuttack. Pp.l-167. Preez, H.H. Du and A. McLachlan. 1984. Biology of the three spot swimming crab, Ovalis punctatus (De Haan) III. Reproduction, fecundity and egg development. Crustacea1Ul41: 285-297. Nikolskii, G.V. 1969. Fish Population Dynamics. Edinburgh: Oliver and Boyd. Translated by J.E.S. Bradley. Novitsky, T.J. 1984. Discovery to commercialization: The blood ofthe horseshoe crab. Oceanus 27: 13-18. Rudloe, A. 1979. Limulus polyphemus. A review of the ecologically significant literature. In Biomedical applicatio of the Horseshoe crab (Limulidae). E. Cohen ecol. Alan. R. Liss. Inc. New York. Pp.27-35. Weeks, S.C. and J.M. Quattro, 199L Life history plasticity under resource stress in a donal fish (Poeciliidae: Poeciliopsis). Journal of Fisheries Biology 39: 485-494. (Received:30 December 1994)